The use of manganese dioxide as an active cathode material (depolarizer) in dry cells is well known. Manganese dioxide for cell use can be formed of natural manganese dioxide ores or it can be electrolytically produced by electrolyzing a manganous sulfate solution as disclosed in the publication titled "Batteries" - Vol. 1, edited by Karl V. Kordesch and published by Marcel Dekker, Inc., New York, 1974. Specifically, the process entails the feeding of a preheated MnSO.sub.4 --H.sub.2 SO.sub.4 bath into an electrolytic cell which is operated with direct current under the following general conditions:
A. electrolyte concentration -- MnsO.sub.4, 0.5 to 1.2 mole/liter; H.sub.2 SO.sub.4, 0.5 to 1.0 mole/liter; PA1 B. electrolyte temperature, 80.degree. C to 100.degree. C.; and PA1 C. an anodic current density of 7 to 12 mA/cm.sup.2.
The anode material generally employed in this type process is titanium, lead alloy or carbon. During electrolysis, the MnSO.sub.4 concentration decreases and the H.sub.2 SO.sub.4 concentration increases in the electrolyte with the net result being that MnO.sub.2 is deposited at the anode and H.sub.2 SO.sub.4 is formed in the electrolyte. The MnO.sub.2 is then removed from the anode and after conventional post-treatment, it is ready for use as an active cathode material in dry cells.
In Russian Inventor's Certificate No. 379,534 to F. K. Andryushchencko et al published July 5, 1973, another electrolytic process is disclosed for the production of electrolytic manganese dioxide which entails the electrolysis of molten manganese nitrate hexahydrate at a temperature of 90.degree. C. to 105.degree. C. and with an anodic current density of 10 to 15 mA/cm.sup.2.
It is an object of the present invention to provide an improvement in the process disclosed in Russian Inventor's Certificate No. 379,534 for producing battery grade MnO.sub.2 from electrolyzed molten Mn(NO.sub.3).sub.2.6H.sub.2 O.
It is another object to provide a process for producing electrolytic manganese dioxide from molten manganese nitrate hexahydrate that will yield manganese dioxide equal to or superior to the commercially available manganese dioxide obtainable from the electrolysis of an aqueous manganous sulfate solution.
Still another object is to provide a process for producing manganese dioxide from molten nitrate manganese hexahydrate whereby manganese dioxide can be deposited on the anodic electrode at a faster rate, i.e. 10 times or more, than the deposition of manganese dioxide using the electrolytic process of an aqueous manganous sulfate solution or the process disclosed in Inventor's Certificate No. 379,534.